Declines in common species

A small number of species typically account for the vast majority of individuals in any given ecological assemblage (the most abundant 25% of species usually comprise >90% of all individuals). These common species are thus often disproportionately important to the functioning and ecosystem processes and service provision of terrestrial and marine ecosystems – because of their sheer numbers, this can be so even when the per capita influence of common species is less than that of rarer ones. They are also the main victims of habitat loss, ecosystem degradation, and overexploitation (indeed changes in their numbers virtually define some of these pressures), and have often experienced huge population and distribution losses. Notwithstanding, and particularly relative to their abundance, these species have often received rather little attention from ecologists and conservation biologists, in favour of research on rarer species. We are studying why common species are common, the roles that they play in ecosystems, and especially their recent declines.